1. Field of the Invention
The present invention relates to a flat metal particle-containing composition suitable to, for example, a heat ray reflection film, an infrared ray reflection film, a visible light reflection film, a heat ray absorption film, an infrared ray absorption film and a selective reflection film; and to a heat ray-shielding material selectively reflecting and absorbing heat rays.
2. Description of the Related Art
Nanoparticles have a size smaller than wavelengths of light and thus attract attention as a material with low light scattering. Among others, research has been made on metal nanoparticles in various fields, since they have electrical conductivity, thermal conductivity, favorable refractive index, catalytic activity, and other features.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2009-215594 discloses that thermal stability of Ag nanowires is improved through mixing with a metal nobler than silver.
Also, JP-A No. 2009-127092 discloses that migration resistance is improved through plating of a metal other than silver.
Although these prior art documents disclose a migration inhibitor or a measure to enhance thermal stability when Ag is used as a conductive material, they neither disclose nor suggest improvement of Ag in light resistance.
Also, the transparent conductive materials disclosed in the above prior art documents utilize conductivity of silver and thus possess problematic sulfurization and oxidization. Meanwhile, in reflective materials utilizing plasmon, a small degree of oxidization or sulfurization on contact points or surfaces does not problematic. Also, other metals could not be used together with silver, since the plasmon wavelength is greatly changed by the other metals.
Moreover, Japanese Patent (JP-B) No. 3594803 discloses a paint utilizing plasmon absorption of a noble metal by mixing a noble metal colloid with a resin. JP-B No. 3594803 neither discloses nor suggests that plasmon of noble metal nanoparticles is unstable for light resistance, since a specific light resistance improver is not used in the noble metal colloid.
Therefore, at present, demand has arisen for provision of a flat metal particle-containing composition in which flat metal particles exist more stably and reduction of plasmon reflection due to light can be prevented; and a heat ray-shielding material which has high selectivity for reflection wavelength or region, has excellent transmittance with respect to visible light and radio wave, and has excellent light resistance.